Wednesday, 21 March 2018

Extreme weather in the Unitee States

Atmospheric River Pummels West Coast as East is Slammed by Yet Another Nor’Easter


20 March, 2018

Today the alerts were sounding in California. Areas recently denuded by extreme wildfires such as Santa Barbara are threatened by debris flows as rainfall amounts of 1-6 inches (up to ten inches locally) are predicted. Meanwhile, the U.S. East Coast braces for the fourth strong nor’easter in three weeks.
Welcome to your weather screwed up by human-caused climate change.
Atmospheric River Brings Landslide Risk to California

Warmer than normal ocean surfaces in the range of 0.5 to 2.5 C hotter than average are bleeding off an excessive volume of moisture across the Northeastern Pacific today. These elevated moisture levels are, in turn, forming into a train of rain-bearing systems aimed fire-hose like at California. This atmospheric river is expected to produce storm after storm after storm. Systems that are predicted to dump between 1 and locally 10 inches of rain over sections of Southwestern California and parts of the Sierra Nevada Range over the next few days.

(An atmospheric river takes aim at California. Image source: MIMIC-TWP.)

These heavier than normal rains are expected to fall over regions hard hit by last summer’s unusually intense wildfires. These fires were both larger and burned hotter than is typical. And, as a result, they have denuded entire regions of trees that previously anchored the soil. Now, with such heavy rains approaching, California is again facing a serious risk of landslides and debris flows.
Fourth Nor’Easter in Three Weeks

As flood and debris flow alerts pop across California, the fourth strong nor’easter to form in three weeks is gathering off the U.S. East Coast. Like the atmospheric river presently taking aim at the West Coast, the nor’easter is gathering over waters that are much warmer than normal — ranging as warm as 9 C above climatological averages in parts of the Gulf Stream off Maine. And it’s also gathering energy from an upper level pattern that has been in place since a major polar warming event rocked the Arctic during February.

(Extremely warm sea surfaces off the U.S. East Coast and in the Gulf of Mexico are providing an extra intensity boost to nor’easters forming across the region. Storms that according to recent science were made two to four times more likely by climate change associated polar warming events. Image source: Earth Nullschool.)

Yesterday, the building storm sparked severe weather across Alabama, Missippi and Georgia — producing large hail, tornadoes and heavy rains. Today, the system is flinging frozen precipitation across the I 95 corridor even as it prepares the batter the East Coast with yet one more bout of gale force winds and heavy seas.
Conditions in Context — The Increasing influence of Climate Change on U.S. Severe Weather

High sea surface temperatures, high atmospheric moisture levels, and a polar-warming linked procession of nor’easters striking the U.S. East Coast are signature influences of human-caused climate change. And each is playing a role, to one degree or another, in the pair of major weather events that are presently developing or underway across the U.S. To wit, the increasingly frequent large fires across the Western U.S. have deforested many hillsides in California and led to the increased risk of debris flows following heavy precipitation events in parts of the state.



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